Indole compounds may be promising medicines for ulcerative colitis
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Indole compounds are extracted from indigo plants and have been used as blue or purple dyes for hundreds of years. In traditional Chinese medicine, herbal agents in combination with Qing-Dai (also known as indigo naturalis) have been used to treat patients with ulcerative colitis (UC) and to remedy inflammatory conditions. Recent studies have noted that indole compounds can be biosynthesized from tryptophan metabolites produced by various enzymes derived from intestinal microbiota. In addition to their action on indole compounds, the intestinal microbiota produce various tryptophan metabolites that mediate critical functions through distinct pathways and enzymes. Furthermore, some indole compounds, such as indigo and indirubin, act as ligands for the aryl hydrocarbon receptor. This signaling pathway stimulates mucosal type 3 innate lymphoid cells to produce interleukin-22, which induces antimicrobial peptide and tight junction molecule production, suggesting a role for indole compounds during the mucosal healing process. Thus, indole compounds may represent a novel treatment strategy for UC patients. In this review, we describe the origin and function of this indole compound-containing Chinese herb, as well as the drug development of indole compounds.
KeywordsInflammatory bowel diseases Ulcerative colitis Chinese herbal medicine Aryl hydrocarbon receptor Indole
We thank the past and present members of the Keio IBD Group for their continued support. We also thank Dr. Kuniki Amano (Sky Clinic, Hiroshima, Japan) for useful suggestions.
Compliance with ethical standards
Conflict of interest
Takanori Kanai received a research grant and lecture fees from Takeda Pharmaceutical Co., Ltd. However, this funding was not related to the generation of this article.
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